Rhodium(I)-catalysed cross-linking of polysiloxanes conducted at room temperature

Abstract

Acetylacetonate and 4-arylimino-2-pentanonate carbonyl complexes of rhodium(I) [Rh(RC(O)C(R’)C(O)R“)(CO)2] (1: R = Me, R’ = H, R'’ = Me; 2: R = Me, R’ = Cl, R'’ = Me; 3: R = Me, R’ = H, R'’ = CO2Me; 4: R = Ph, R’ = H, R'’ = Me; 5: R = Ph, R’ = H, R'’ = Ph) and [Rh(MeC(NR’’’)CHC(O)Me)(CO)2] (6: R’'’ = Ph; 7: R’'’ = 2,6-Me2C6H3) were examined as hydrosilylation cross-linking catalysts at RT for the reaction of poly(dimethylsiloxane-co-ethylhydrosiloxane) copolymer with vinyl terminated poly(dimethylsiloxane) or vinyl terminated poly(dimethylsiloxane-co-styrene) copolymer. All complexes allow cross-linking of vinyl- and hydride-containing polysiloxanes and copolymers at RT without inhibitor addition. Complexes 1–7 possess catalytic activity comparable to the industrially used complex of Pt0 and divinyltetramethyldisiloxane (Karstedt's catalyst). 1 is the most active among the studied rhodium complexes at 1.0 × 10−4 mol⋅L−1 and 1.0 × 10−5 mol⋅L−1. Silicone rubbers obtained with the rhodium catalysts compared to Karstedt's catalyst possess no visible defects (bubbles or cracks), and differed by improved elastic properties (the elongation at break increased from 160 to 255%) The activity and improved silicone rubber properties using 1 renders it one of the suitable alternatives to Karstedt's catalyst.